The effects of ionizing irradiation and frying on the thiamine and ribojlavin content of bacon were determined. Signijicant destruction of thiamine but not ribojavin occurred during both the irradiation and frying. The destruction of thiamine was found to be directly related to the dose of ionizing radiation or the degree of cooking. Frying before irradiation, reduction of water content by lyophilization, and irradiation at -40°C rather than 2°C produced signijicantly greater retention of thiamine. Frying the bacon following irradiation produced radiation dose-related, nonadditive, increased destruction of thiamine. The protective effect offring before irradiation was not directly linked with the reduction of moisture by h i n g .